Aviation safety investigations & reports

Boeing Co 737-700, VH-VBU

Summary

On 14 April 2005, an Aero Commander 500-S aircraft, registered
VH-YJR, departed Brisbane aerodrome on a non-scheduled flight to
Maryborough, Qld. It passed within 1 NM horizontally and 500 ft
vertically of a Boeing Company 737-76Q (737) aircraft, registered
VH-VBU, that was inbound from Darwin, NT, on a scheduled passenger
service.

Factual Information

Sequence of events

On 14 April 2005, an Aero Commander 500-S aircraft, registered
VH-YJR, departed Brisbane aerodrome on a non-scheduled flight to
Maryborough, Qld. It passed within 1 NM horizontally and 500 ft
vertically of a Boeing Company 737-76Q (737) aircraft, registered
VH-VBU, that was inbound from Darwin, NT, on a scheduled passenger
service.

The Aero Commander became airborne off runway 32 at 0543 Eastern
Standard Time, 4 minutes after the nominated first light for
Brisbane aerodrome. The Brisbane aerodrome controller had
instructed the pilot of the Aero Commander to turn right, once
airborne, onto a heading of 090 degrees and to climb to 2,000 ft.
The pilot complied with the departure instructions and contacted
the approach controller on the approach frequency. The approach
controller acknowledged that broadcast and asked the pilot for
'good forward speed'.

The crew of the 737 were on the approach frequency and were
positioning the aircraft for final approach to runway 19. Although
the pilot of the Aero Commander and the crew of the 737 were on the
approach frequency, the aerodrome controller confirmed with the
approach controller that he was visually separating both aircraft
as had been previously agreed. The aerodrome controller later
reported that he was expecting the approach controller to assign a
heading of 360 degrees to the pilot of the Aero Commander.

The approach controller passed traffic information to the pilots
of both aircraft and the Aero Commander pilot sighted the 737 soon
after. At 0544:20 the crew of the 737 reported that they were
established on the final approach path for runway 19. The approach
controller advised them that the Aero Commander was going to cross
the runway 19 final approach path and that the tower was providing
visual separation.

The aerodrome controller became concerned about the separation
between the two aircraft and at 0544:50 asked the approach
controller to instruct the pilot of the Aero Commander to turn left
20 degrees. That instruction was passed and the Aero Commander
pilot complied. The aerodrome controller was still concerned and
asked the approach controller to instruct the pilot of the Aero
Commander to make an immediate hard left turn onto a heading of 360
degrees. The approach controller advised the aerodrome controller
that he was concerned about that heading and did not transmit the
instruction.

By 0545:26 the aerodrome controller considered that the Aero
Commander had crossed the runway 19 final approach path. In
response to a request by the approach controller, the pilot of the
Aero Commander confirmed that he could see the 737, but at that
stage the 737 crew had not seen the Aero Commander. Not long after
that, the 737 crew saw the Aero Commander and were subsequently
transferred to the Brisbane tower frequency. Figure 1 shows the
position of the two aircraft as the Aero Commander crossed the
final approach path at 0545:30.

Figure 1: Relative flight paths of the Aero Commander and
the 737 as the Aero Commander crossed the final approach path of
runway 19 at 05:45:30

A review of the recorded radar data showed that separation between
the aircraft reduced to a minimum of 0.95 NM horizontally, at which
time vertical separation had reduced to 500 ft.

Noise abatement procedures

The noise abatement procedures applicable at Brisbane at the
time of the occurrence specified that all aircraft departing runway
32 between 2200 and 0600 must be contained within a sector of
airspace between 360 and 120 degrees, over water, until leaving
5,000 ft. A heading of 360 degrees for a departure from runway 32
would have complied with those requirements.

To comply with the noise abatement procedures, runway 19 was the
nominated duty runway for arrivals, and runway 01 was the nominated
duty runway for departures. Pilots were also advised, on the
automatic terminal information service, to obtain approval from air
traffic control prior to starting engines. The requirement for a
start clearance in thesecircumstances was in accordance with the
Manual of Air Traffic Services (MATS) and enabled any delays to be
absorbed on the ground before an aircraft's engines were
started.

The aerodrome controller issued a start clearance to the pilot
of the Aero Commander. The aerodrome controller did not coordinate
the start clearance with the approach controller, nor was he
required to do so. The ADC was required to review the disposition
of inbound traffic when making a decision as to the timing of a
start clearance.

The approach controller reported that he instructed the
aerodrome controller to assign a departure heading of 090 to the
pilot of the Aero Commander to ensure compliance with the noise
abatement procedures.

Air traffic control separation standards and
procedures

Control of aircraft in the Brisbane aerodrome terminal area was
provided by an aerodrome controller located in the control tower
using visual procedures, or by an approach controller using radar
information. The MATS stated that the primary role of aerodrome
controllers was to maintain visual observation of aircraft
operations. Coordination of responsibilities and roles was required
between the aerodrome controller and the approach controller, and
formal guidelines were specified in a letter of agreement. The
letter of agreement stated in part that:

In visual conditions, separation is achieved by the application
of a radar standard or the provision of visual separation.

It also stated that:

In the application of visual separation, BNT [Brisbane aerodrome
controller] shall ensure that separation in azimuth
1 is maintained until the establishment of a radar or
procedural separation standard … In all situations where BNT is
providing visual separation, traffic that will operate in close
proximity will be retained on TWR [tower] frequency.

Although the aerodrome controller transferred the pilot of the
Aero Commander to the departures frequency, the approach controller
did not accept separation responsibility for the aircraft after the
737 was established on the runway 19 final approach path. He
reported that he may not have been able to maintain the minimum
radar separation standard of 3 NM horizontally, or 1,000 ft
vertically.

The aerodrome controller reported that he accepted
responsibility for visual separation between the two aircraft once
the 737 was established on the runway 19 final approach path,
because he had a 'mindset' that the Aero Commander was going to
turn right onto a heading of 360 degrees once airborne. The
aerodrome controller later reported that he would not have accepted
responsibility for separation if he had realised that the approach
controller had assigned a heading of 090 degrees, because that
heading would not have enabled him to maintain visual separation
between the two aircraft. Although the pilot of the Aero Commander
advised the approach controller that he had the 737 in sight, the
approach controller did not assign responsibility for separation to
the pilot of the Aero Commander. There was an infringement of
separation standards.

The information in the letter of agreement was supported by the
Manual of Air Traffic Services (MATS), which contained procedures
to be used by air traffic controllers. Paragraph 4.5.2.8 (effective
10 June 2004) stated that:

In providing visual separation, controllers should rely
primarily on azimuth. Visual separation by judgement of relative
distance or height shall be used only with such wide margins that
there is no possibility of the aircraft being in close
proximity.

The Brisbane tower was equipped with a radar display that
provided the aerodrome controller with the same traffic display
that was provided to the approach controller. The MATS addressed
the use of tower radar in an aerodrome control service. It stated
that the tower radar display was available for the determination of
the altitude, position, or tracking of aircraft to establish or
monitor separation. However, the MATS also stated that:

…the use of Tower radar should not impinge upon an aerodrome
controller's primary function of maintaining a visual observation
of operations on and in the vicinity of the aerodrome.

The MATS also stated that separation assurance could be achieved
through planning traffic to ensure separation, executing the plan
to achieve separation and monitoring the situation to ensure that
the plan and the execution are effective.

Aerodrome controller

The aerodrome controller was trained and rated for the aerodrome
control function at Brisbane. At the time of the occurrence he was
nearing the end of a night shift which had commenced at 2200 the
previous day. He reported that there had been a data upgrade to The
Australian Advanced Air Traffic System during the night. The
aerodrome controller considered that the data upgrade resulted in a
higher workload than a standard night shift.

The aerodrome controller reported that, at the time of the
occurrence, he felt fatigued. He also reported that he was feeling
slightly unwell, but that he considered himself fit for duty. He
was sleeping adequately and, apart from the slight illness, there
were no indications of any personal, physiological or medical
issues that were likely to have influenced the controller's
performance.

Meteorological information

The weather information being broadcast to pilots for Brisbane
Airport at the time of the occurrence advised that the visibility
was greater than 10 km, that there were showers in the area and
some cloud at 2,500 ft. The wind was reported as 180 degrees at 8
kts, with a maximum downwind of 10 kts on runway 01.

1. Horizontal bearing or
direction.

Analysis

ANALYSIS

Introduction

Although there was no specified minimum distance standard for
visual separation in these circumstances, the aerodrome controller
was unable to continue to apply a visual separation standard, in
azimuth, between the 737 and the Aero Commander. This analysis
examines the development of the occurrence and highlights the
safety issues that became evident as a result of the
investigation.

Noise abatement procedures

Airspace restrictions imposed by the noise abatement procedures
in force at the time of the occurrence resulted in limited options
available to either the aerodrome controller or the approach
controller to separate the departing Aero Commander with the
inbound aircraft. The approach controller determined that he would
be unable to establish and maintain a separation standard between
the two aircraft and comply with noise abatement procedures, and so
relied on the aerodrome controller to separate the two aircraft
using visual separation.

The requirement for pilots to request a start clearance would
normally provide the aerodrome controller with an opportunity to
assess the traffic situation, in light of airspace limitations
associated with noise abatement procedures, so that any delays can
be absorbed prior to the aircraft's engines being started. A
heading of 360 degrees was an appropriate heading in the
circumstances. It would also have complied with noise abatement
procedures and facilitated the application of visual separation in
azimuth.

Controllers cannot be held responsible for delays to departing
aircraft as a result of noise abatement procedures. Controllers are
required to take such restrictions into account in their normal
decision making processes. The noise abatement procedures
themselves were not considered to have contributed significantly to
this occurrence.

Air traffic control separation standards and procedures

The converging tracks of the two aircraft precluded the
aerodrome controller from ensuring that visual separation, in
azimuth, was not infringed.

The low light conditions at that time of day and the cloud
cover, may have made it difficult for the aerodrome controller to
visually determine the departure track of the Aero Commander.
Reference to the tower radar display was authorised by the Manual
of Air Traffic Services (MATS) and would have clearly indicated the
Aero Commander's track. Had the aerodrome controller referred to
the tower radar display earlier, he may have been able to take
action in sufficient time to ensure that separation was not
infringed.

The situation which arose, where the aerodrome controller was
separating the aircraft while the aircraft were not on the
aerodrome control frequency, was not consistent with the letter of
agreement. However, it did enable the approach controller to
provide mutual traffic information to the pilots of both aircraft.
That increased the awareness of the 737 crew of the presence of the
Aero Commander, and assisted the pilot of the Aero Commander to see
the 737.

Although it would have been difficult for the aerodrome
controller to separate the departing Aero Commander on a heading of
090 degrees, with arriving aircraft on the final approach path for
runway 19, the aerodrome controller accepted those instructions and
confirmed that he could separate in those circumstances. On that
basis, the approach controller authorised the departure. The
approach controller coordinated the departure instructions with the
aerodrome controller in accordance with the letter of agreement.
The approach controller confirmed, on a number of occasions, that
the aerodrome controller had accepted responsibility for separating
the Aero Commander on a heading of 090 degrees. The approach
controller had no way of knowing that the aerodrome controller had
misunderstood the instruction.

From the aerodrome controller's perspective, a heading of 360
degrees off runway 32 was appropriate given the disposition of the
arriving aircraft. It would also have complied with the noise
abatement procedures and enabled him to visually separate the Aero
Commander in azimuth with the 737, once the 737 was established on
the final approach path.

The aerodrome controller's subsequent request for a 20 degree
left turn for the Aero Commander is difficult to reconcile. The
resultant heading of 070 degrees turned the Aero Commander towards
the 737 and does not appear to be consistent with a resolution of
the developing confliction. By that time the aerodrome controller
could not have been certain from visual observation that the
aircraft were not in close proximity.

The investigation was unable to determine why the aerodrome
controller had a 'mindset' that the Aero Commander was departing on
a heading of 360 degrees, when that option was never discussed or
coordinated with the approach controller. The higher workload that
was reported to have resulted from The Australian Advanced Air
Traffic System data upgrade may have had an adverse effect on the
aerodrome controller's cognitive processes towards the end of the
night shift. The possibility that fatigue contributed to the
occurrence could not be discounted.

Safety Action

SAFETY ACTION

As a result of this occurrence, Airservices Australia proposed
the following system improvements:

At the time of writing this report, the Bureau had not received
advice from Airservices Australia regarding the status of these
proposals.
On 20 December 2005, Airservices Australia advised the ATSB of the
following safety actions:

Knowledge of reciprocal runway operations is tested during
assessments;